Experiment - The Effect of Temperature and pH on Enzyme Action

Test tube	Contents	Iodine Test: 0min	Iodine Test: 10min	Conclusion
W	2cm3 of starch solution + 2cm3 of HCl + 2cm3 of amylase	Solution turned blue-black	Mixture turned blue-black	Enzymes cannot function in very low pH
X	2cm3 of starch solution + 2cm3 of distilled water + 2cm3 of amylase	Solution turned brown with traces of blue black	Mixture turned brown with traces of blue-black	Enzymes work well in neutral pH
Y	2cm3 of starch solution + 2cm3 of NH4OH + 2cm3 of amylase	Solution turned blue-black	Mixture turned blue-black with traces of brown	Enzyme action is little when pH is high
Z	2cm3 of starch solution + 4cm3 of distilled water	Solution turned blue-black	Mixture turned blue-black	Starch is not broken down as enzymes were not added to the solution

Table 2 - Results of starch digestion using amylase in different pH

INTERPRETING THE RESULTS
1. Which test-tube shows that starch digestion has occurred? Give your reasons.
Test-tube X, as the iodine solution turned brown with traces of blue-black when added to the mixture, indicating that there is little starch left in the mixture, and hence showing that amylase has broken down the starch.

2. Which of the test-tubes contained mixtures that gave a blue-black colour?
Test-tubes W, Y and Z.

3. Why did the mixtures in tubes stated in (2) remain blue-black?
For tubes W and Y, they remained blue-black as the pH conditions of the mixtures were not suitable for amylase to carry out starch digestion. For tube Z, it is a control setup and hence the starch is unaffected.

4. What conclusion(s), based on the observations in this experiment, can be made about the effect of pH on enzyme action?
Extreme pH (too high or too low) causes enzymes to be unable to function.


PART 1

Test tube	Contents	Temperature	Iodine Test	Conclusion
A1	A1: starch solution A2: amylase solution	0 degrees Celsius	Mixture turned blue-black with traces of brown	Enzyme action is reduced with low temperature
B1	B1: starch solution B2: amylase solution	37 degrees Celsius	Mixture turned brown with traces of blue-black	Enzyme action is high
C1	C1: starch solution C2: amylase solution	100 degrees Celsius	Mixture turned blue-black	There is almost no enzyme action as the temperature is too high for enzymes to function
D1 (control setup)	D1: starch solution D2: distilled water	37 degrees Celsius	Mixture turned blue-black	Starch is not broken down as enzymes were not added to the solution

Table 1 - Results of starch digestion using amylase at different temperatures

INTERPRETING THE RESULTS
1. Which tube shows that starch digestion has occurred? Give your reasons.
Tube B1, as the iodine solution turned brown with traces of blue-black when added to the solution, indicating that there is little starch left in the solution. This shows that the amylase in the tube has broken down the starch.

2. Which of the test-tubes contained mixtures that gave a blue-black colour?
Test-tubes A1, C1 and D1.

3. Why did the mixtures in tubes stated in (2) remain blue-black?
For tubes A1 and C1, they remained blue-black as the temperature was too low and too high respectively for amylase to function properly and digest starch. For D1, however, no amylase was present to break down starch so the starch was unaffected.

4. What purpose did the tube D1 serve?
It served as a control.

5. Using your knowledge of the structure of starch, describe the test you would use to detect the presence of the substance produced as a result of the reaction in test tube stated in (1) above.
I would use Benedict's Test for reducing sugars, as starch should be broken down into monosaccharides which are reducing sugars.

6. What conclusion(s), based on the observations in this experiment, can be made about the effect of temperature on enzyme action?
Extreme temperatures (too high or too low) causes enzymes to be unable to function.